Volume control for audio signals

ABSTRACT

A motion picture soundtrack reproduction system has a center front soundtrack channel and a plurality of other soundtrack channels. A volume control adjusts the gain of all the channels. The volume control has a range of settings from a minimum to a maximum, the gain of the center front channel having substantially a first relationship to the volume control settings and the gain of the other channels having substantially a second relationship to the volume control settings, the relationships being such that for a range of volume control settings less than a first setting the gain of the center front channel remains substantially constant while the gain of the other channels decreases as the setting decreases or decreases more gradually than the gain of the other channels as the setting decreases.

TECHNICAL FIELD

The invention relates generally to the processing of audio signals. Moreparticularly, the invention relates to control of the loudness of motionpicture soundtracks when reproduced.

BACKGROUND ART

In the mid-1970s, Dolby Laboratories introduced a calibrationrecommendation for monitor levels in movie soundtracks (“Dolby” is atrademark of Dolby Laboratories, Inc.). A pink noise reference signalwas used in the record chain to adjust the audio monitor level to 85dBc. All theatres equipped for playback of the new stereo opticalsoundtracks were set up such that an equivalent pink noise signal in asoundtrack channel generated the same 85 dBc with the playback volumecontrol (fader) set to the calibrated setting. This meant that theatresplaying films at the calibrated volume control setting (a setting of “7”in a range of “0” to “10” on most cinema processors) reproduced the sameloudness level selected by the film director and audio engineers in thedubbing theatre (referred to herein as “the mixer”).

This system worked quite well for many years. Dolby Stereo (A-typeencoded) films had limited headroom and the resulting constraineddynamic range yielded few audience complaints. Most theatres playedfilms at the calibrated level. Soundtrack format technology has beensignificantly enhanced since Dolby Stereo. Dolby SR extended theheadroom by 3 dB at midrange frequencies, and more at low and highfrequencies. In recent years, the new digital formats have furtherincreased the headroom. FIG. 1 shows maximum sound pressure level of onereproduced soundtrack channel versus frequency for four photographicsoundtrack formats, Academy mono, Dolby A-type, Dolby SR and DolbyDigital. The curves are normalized with respect to their referencelevels. Thus, they show the maximum sound pressure level that onechannel of each different optical soundtrack system is capable of whenplaying a motion picture at the calibrated volume control setting in aproperly set up theater. The maximum sound pressure level in a theateris also a function of the number of soundtrack channels. For example,five channels can deliver 2.5 times as much power as two channels,resulting in an increase of 4 dB in sound pressure level. Thus, in thecase of five or seven channel digital soundtrack reproduction, forexample, the increase in peak sound pressure level is even greater thanthat shown in FIG. 1.

Because the 85 dBc calibration technique has been maintained throughoutevolving format changes, additional headroom is available on the newersoundtracks. However, feature films do have a consistent, subjective mixreference, independent of increased headroom, for dialogue record level,known as “associative loudness.” When the dubbing mixer sees an actor onthe screen, and there is no conflict between the dialogue and music oreffects, the dialogue level in a moderate close-up is set to beplausible for the visual impression. Within reasonable limits, thisgenerally holds true to within 2 or 3 dB. This natural dialogue leveldoes not hold true for narration, as there is no corresponding visualreference. Music and effects have no direct visual associative loudness.Most people are not familiar with the actual sound pressure levels of aConcorde takeoff or a 50 mm howitzer. The music score level is equallyuncalibrated.

As the headroom capability of the recording medium has been extended, ithas certainly been used: the “non-associative” loudness of effects andmusic has risen to fill the available headroom space. Using dialogue asa reference, loud sounds like explosions are often 20 dB or more louder(explosions reach full scale peak level of 25 dB above dialogue level),and some quiet sounds, which are intended to be heard by all listeners,such as leaves rustling, may be 50 dB quieter.

In response to audience complaints that movies are too loud, manytheatres are playing films substantially below the calibrated level. Avolume control setting (fader level) of “6” or “5½,” as opposed to thecalibrated level (volume control standard setting) of “7,” is notuncommon, representing a loudness reduction of approximately 4 or 6 dB.Some cinemas have their volume control permanently turned down to suchsettings because projectionists operating multiplexes with many screensshowing different movies simultaneously don't have the time or cannot bebothered to set the controls differently for different movies. If thevolume control is turned down to avoid complaints of excessive loudness,the dialogue is quieter than the mixer intended, and audiences maycomplain instead that some dialogue is not intelligible in the presenceof other sounds in the film and/or general background noise of thetheater (popcorn eating, air-conditioning, people talking, etc.).Theatre playback levels are often set by complaints generated by theloudest (and earliest) element of the show. If the playback level is setin response to the loudest trailer (preview), which is often louder thanthe feature film, the feature often plays at the same reduced level. Theresult is that the dialogue level of the feature is lowered by the samelevel deemed necessary to attenuate the trailer. A feature film playedwith a loudness 6 dB below the calibrated level may have seriousdialogue intelligibility problems and very quiet sounds may becomeinaudible.

In addition, it is possible that the increased use of headroom fromDolby A-type to Dolby SR and digital releases has not been matched by acorresponding increase in power amplifier and loudspeaker capability.The resultant distortion from overloaded equipment may well exacerbatethe loudness problems of recent soundtracks, causing increased incidenceof complaints.

In early cinema sound equipment employing calibration, the volumecontrol was a mechanical potentiometer, often with a click-stop ordetent at the standard setting. More recent (digital) equipment uses ashaft encoder or a pair of up-down buttons (with a numeric display forthe setting), delivering a control signal that operates on multipliers(either digital or voltage-controlled amplifiers) to affect the gainapplied to all channels of the reproduced soundtracks. In typical cinemasound equipment, the volume control varies the gain gradually andrelatively uniformly over a range of settings from about “4” to “10,”with the gain falling more rapidly at setting below about “4,” allowinga fade to inaudibility. Such a typical prior art relationship betweengain or loss and volume control setting is shown in the lower curve ofFIG. 2, described below.

With the exception of monophonic installations, to which the presentinvention does not apply, all movie sound installations include three ormore front loudspeakers including a center front. Historically, filmmixers place dialogue in the center front channel and it is rare forspeech from an on-screen actor to be placed anywhere else. This appliesboth for a multitrack digital soundtrack (for instance 5.1- or7.1-channels) or a two-channel analog optical soundtrack reproduced viaa matrix decoder to derive left, center, right and surround outputs. Thecenter front channel may of course contain other material, but,generally, it is material important in following the action of the moviebecause the audience's attention is focused on the screen. At momentswhen the soundtrack is loud enough to provoke complaint, severalchannels are generally contributing to that loudness, not just any one,and in particular not just the center front.

DISCLOSURE OF INVENTION

In accordance with the present invention, a motion picture soundtrackreproduction system comprises a center front soundtrack channel and aplurality of other soundtrack channels. A volume control adjusts thegain of all the channels, the volume control having a range of settingsfrom a minimum to a maximum, the gain of the center front channel havingsubstantially a first relationship to the volume control settings andthe gain of the other channels having substantially a secondrelationship to the volume control settings, the relationships beingsuch that for a range of volume control settings less than a firstsetting the gain of the center front channel remains substantiallyconstant while the gain of the other channels decreases as the settingdecreases or decreases more gradually than the gain of the otherchannels as the setting decreases.

Also in accordance with the present invention, a motion picturesoundtrack reproduction system comprises a center front soundtrackchannel and a plurality of other soundtrack channels, each of thechannels having adjustable gain and one or more loudspeakers, and acontroller having a volume control for adjusting the gain of all thechannels, the volume control having a range of settings from a minimumto a maximum, the gain of the center front channel having a firstrelationship to the volume control settings and the gain of the otherchannels having a second relationship to the volume control settings,the relationships being such that for a range of volume control settingsless than a first setting the gain of the center front channel remainssubstantially constant while the gain of the other channels decreases asthe setting decreases or decreases more gradually than the gain of theother channels as the setting decreases.

The range of volume control settings less than the first setting extendsdown to the minimum control setting or, alternatively, down to a secondsetting above the minimum control setting. In the latter case, forsettings less than the second setting the gains of all the channelsdecrease in substantially the same way as the setting decreases and forsuch volume control settings the gain of the center front channel isgreater than the gain of the other channels. Optionally, for settingsless than the second setting the gain of the center front channel isgreater than the gain of the other channels by a substantially constantamount in the logarithmic domain.

For settings greater than the first setting the gains of all thechannels may increase as the setting increases and for each of suchvolume control settings the gain of the center front channel and thegain of the other channels may be substantially the same.

The invention is particularly advantageous in an arrangement in whichwhen the volume control is set to a standard setting, each of thechannels has a respective gain that produces a respective standardacoustic level in response to a signal having a respective standardreference level in the channel. In that case, the first setting is aboutthe standard setting.

The invention provides for reducing the maximum loudness, and therebyavoiding complaints, while maintaining the acoustic level of the centerfront containing dialogue and requiring only one user-operated control.According to an embodiment of the invention, the cinema equipment isdesigned and installed in the conventional manner to the extent thatwith the volume control nominally at its standard setting, each of thereproduced soundtrack channels has a respective gain that produces arespective standard acoustic level in response to a signal having arespective standard reference level in the channel, thus matching thestandard levels in a film mixing room. Thus, when calibrated, theplayback system with its volume control at the standard setting has anapparent loudness that is substantially the same as that intended by thefilm mixer. However, in accordance with the present invention, if thevolume control is turned down below the standard setting in response toactual (or expected) complaints from the audience, over a limited rangeof settings all channels except the center front are attenuated equally,but the center front is reduced by a smaller degree (or not at all). Theeffect is not only a reduction in the overall loudness but an increasein the proportionate contribution of the center front channel, with apotential improvement in intelligibility when the other channels areloud. Optionally, after some degree of changing the balance of thecenter front to other channels down to a setting below the standardsetting, for further lowering of the settings all channels areattenuated equally, maintaining fixed the altered balance.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows maximum sound pressure level versus frequency for fourphotographic soundtrack formats, Academy mono, Dolby A-type, Dolby SRand Dolby Digital.

FIG. 2 shows one set of suitable relationships between gain of thecenter front soundtrack channel and gain of each of the other soundtrackchannels versus volume control setting, in which a gain of 0 dB isobtained for the standard volume control setting.

FIG. 3 is a simplified block diagram showing an implementation of thepresent invention from a structural standpoint.

FIG. 4 is a simplified block diagram showing an implementation of thepresent invention from a functional standpoint.

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 2 illustrates idealized curves of gain/loss as a function of volumecontrol setting, for the center front channel (upper line) and for eachof the remaining channels (lower line). The lower line also shows thetypical gain/loss for all channels (rather than channels other than thecenter front channel, as in the present invention) as a function ofvolume control setting in prior art motion picture sound equipment.While the characteristic responses shown in the example of FIG. 2 arepractical and useful ones, the precise characteristics are not critical.For example, the lower characteristic curve need not be the same as inthe prior art gain/loss for all channels versus volume control settingThe characteristics shown in the figures are just one example ofsuitable characteristics that fall within the scope of the invention

Still referring to FIG. 2, it will be seen that the gain of the centerfront channel has a first relationship to the volume control settingsand that the gain of each of the other channels has a secondrelationship to the volume control settings. In FIG. 2, 0 dB is definedas the gain with the volume control at a first setting, the standard “7”setting. As shown in FIG. 2, for settings less than the first settingdown to a second setting, the gain of the center front channel decreasesmore gradually than the gain of the other channels as the settingdecreases. Alternatively, over a limited range of settings just belowthe standard setting, for instance between a setting of “7” and asetting of “6,” the center channel gain may be constant as the gain ofthe other channels changes. Although such changes in gain (eitheralternative) may extend down to the minimum volume control setting, in apractical embodiment such changes in gain preferably do not extend downto the minimum setting but rather to a second setting, which may be asetting of about “5,” for example, as shown in FIG. 2. In that case, forsettings below the second setting, the gains of all the channelsdecrease in substantially the same way as the setting decreases and forsuch volume control settings the gain of the center front channel isgreater than the gain of the other channels by a few dB, for example, asshown in FIG. 2. Preferably, for settings above the nominal standardsetting up to a maximum setting, the gains of all the channels increaseas the setting increases and for each of such volume control settingsthe gain of the center front channel and the gain of the other channelsare substantially the same. It should be understood that therelationships between the gain of the center front channel, on one hand,and the gain of the other channels, on the other hand, versus the volumecontrol settings need not be precisely in accordance with the examplesof FIG. 2, but are to be limited only by the scope of the appendedclaims.

An exemplary system according to the present invention is shown in FIG.3. A center front soundtrack channel has a gain adjuster 102 thatcontrols the gain of the channel. The channel feeds one or moreloudspeakers 104 via a power amplifier (not shown). In practice, thegain adjuster 102 may be, for example, the gain or volume control of apreamplifier or a passive variable loss at the output (preferably theoutput rather than the input) of a preamplifier. A plurality of otherchannels, shown for simplicity as two channels, each has a respectivegain adjuster 106 and 108. Each channel feeds one or more respectiveloudspeakers 110 and 112 via respective power amplifiers (not shown).The gain adjuster 102 for the center front channel is controlled by afirst output of a controller 114 and the gain adjusters 106 and 108 forthe other channels are controlled by a second output of controller 114,in the manner described herein in response to the setting of thecontroller's volume control 116.

In a practical arrangement employing digital controls, as shown in FIG.4, the volume control setting may select values in first and secondlookup tables 202 and 204. The first lookup table 202 in turn may adjusta multiplier controlling volume 206 in the center front channel, whilethe second lookup table 204 may adjust multipliers controlling volume208 and 210 in the other channels. Lookup table values in response tovolume control settings may be chosen so as to provide the desiredrelationships between gains in the various channels versus setting.

The present invention and its various aspects may be implemented inanalog circuitry, for example, with two suitable non-linear functionsrelating control setting to gain, or as software functions performed indigital signal processors, programmed general-purpose digital computers,and/or special purpose digital computers, or some combination of suchdevices and functions. Interfaces between analog and digital signalstreams may be performed in appropriate hardware and/or as functions insoftware and/or firmware.

The invention claimed is:
 1. A motion picture soundtrack reproductionsystem, the system having a center front soundtrack channel and aplurality of other soundtrack channels, comprising: a controller havinga volume control for adjusting the a gain of all the channels for thecenter front channel and a gain for the plurality of other channels, thevolume control having a range of settings from a minimum to a maximum,the controller having a first output for controlling the gain of thecenter front channel and a second output for controlling the gain of theplurality of other channels in response to settings of the volumecontrol, the gain of the center front channel having a firstrelationship to the volume control settings and the gain of theplurality of other channels having a second relationship to the volumecontrol settings, the first relationship and the second relationshipsbeing such that for a range of volume control settings less than a firstsetting the gain of the center front channel (1) remains substantiallyconstant while the gain of the plurality of other channels decreases asthe a volume control setting decreases below said first setting, or (2)decreases more gradually than the gain of the plurality of otherchannels as the volume control setting decreases below said firstsetting.
 2. A motion picture soundtrack reproduction system, comprising:a center front soundtrack channel and a plurality of other soundtrackchannels, each of said channels having adjustable gain and feeding oneor more loudspeakers, and a controller having a volume control foradjusting the gain of all the channels a gain for the center frontchannel and a gain for the plurality of other channels, the volumecontrol having a range of settings from a minimum to a maximum, thecontroller having a first output for controlling the gain of the centerfront channel and a second output for controlling the gain of theplurality of other channels in response to settings of the volumecontrol the gain of the center front channel having a first relationshipto the volume control settings and the gain of the plurality of otherchannels having a second relationship to the volume control settings,the first relationship and the second relationships relationship beingsuch that for a range of volume control settings less than a firstsetting the gain of the center front channel (1) remains substantiallyconstant while the gain of the plurality of other channels decreases asthe a volume control setting decreases below said first setting or (2)decreases more gradually than the gain of the plurality of otherchannels as the volume control setting decreases below said firstsetting.
 3. A system according to claim 1 or claim 2 wherein the rangeof volume control settings less than said first setting extends down tothe minimum volume control setting.
 4. A system according to claim 1 orclaim 2 wherein the range of volume control settings less than saidfirst setting extends down to a second setting above the minimum volumecontrol setting.
 5. A system according to claim 3 4 wherein for volumecontrol settings less than said second setting the gains of all thechannels decrease in substantially the same way gain of the center frontchannel and the gain for the plurality of other channels are attenuatedequally as the volume control setting decreases below said secondsetting and for such volume control settings the gain of the centerfront channel is greater than the gain of the plurality of otherchannels.
 6. A system according to claim 5 wherein for volume controlsettings less than said second setting the gain of the center frontchannel is greater than the gain of the plurality of other channels by asubstantially constant amount in the logarithmic domain.
 7. A systemaccording to claims 1 wherein for volume control settings greater thansaid first setting the gains of all the channels gain for the centerfront channel and the gain for the plurality of other channels increaseas the volume control setting increases above said first setting and foreach of such volume control settings the gain of the center frontchannel and the gain of the plurality of other channels aresubstantially the same.
 8. A system according to claims 1 wherein whenthe volume control is set to a standard setting, each of the centerfront channel and the plurality of other channels has a respective gainthat produces a respective standard acoustic level in response to asignal having a respective standard reference level in the channel.
 9. Asystem according to claim 8 wherein said first setting is about saidstandard setting.
 10. An audio system comprising: a first channel, again of the first channel adjustable by a controller; a second channel,a gain of the second channel adjustable by the controller; and thecontroller including: a volume control having a first range of settingsfrom a minimum to a maximum; a first output controlling the gain of thefirst channel in response to a setting of the volume control; and asecond output controlling the gain of the second channel in response tothe setting of the volume control, wherein a decrease in the setting ofthe volume control both decreases loudness of the system and increases aproportionate contribution of the first channel to the loudness.
 11. Asystem of claim 10 wherein the second output further controls a gain fora third channel in response to the setting of the volume control.
 12. Asystem of claim 10 further comprising at least one loudspeaker.
 13. Asystem of claim 10 further comprising surround outputs.
 14. An audioreproduction system comprising: a first channel, a gain of the firstchannel adjustable by a controller; a second channel, a gain of thesecond channel adjustable by the controller; and the controllerincluding: a volume control having a first range of settings from aminimum to a maximum; a first output for controlling the gain of thefirst channel in response to a setting of the volume control; and asecond output for controlling the gain of the second channel in responseto the setting of the volume control, wherein the gain of the secondchannel decreases more than the gain of the first channel inrelationship with a decrease in the setting of the volume control over asecond range, the second range being smaller than the first range.
 15. Asystem of claim 14 wherein the second output further controls a gain fora third channel in response to the setting of the volume control, andthe gain of the third channel decreases more than the gain of the firstchannel in relationship with the decrease in the setting of the volumecontrol over the second range.
 16. An audio system comprising a firstchannel and a second channel, each of said channels having a gain; and acontroller having a volume control for adjusting the gain of the firstchannel and the gain of the second channel, the volume control having arange of settings from a minimum to a maximum, the gain of the firstchannel having a first relationship to the volume control settings andthe gain of the second channel having a second relationship to thevolume control settings, the relationships being such that for a rangeof volume control settings less than a first setting the gain of thefirst channel (1) remains constant while the gain of the second channeldecreases as the volume control setting decreases below said firstsetting or (2) decreases more gradually than the gain of the secondchannel as the volume control setting decreases below said firstsetting.
 17. A system according to claim 16 wherein the range of volumecontrol settings less than said first setting extends down to theminimum control setting.
 18. A system according to claim 16 wherein therange of volume control settings less than said first setting extendsdown to a second setting above the minimum volume control setting.
 19. Asystem according to claim 18 wherein for volume control settings lessthan said second setting the gains of the first and second channels areattenuated equally as the volume control setting decreases below saidsecond setting and for such volume control settings the gain of thefirst channel is greater than the gain of the second channel.
 20. Asystem according to claim 19 wherein for volume control settings lessthan said second setting the gain of the first channel is greater thanthe gain of the second channel by a constant amount in the logarithmicdomain.
 21. A system according to claim 16 further comprising left,right and surround outputs.